• Heparan sulfates [HS; sulfated GlcNAc(α1-4)GlcA/IdoA(β1-4)] and chondroitin/dermatan sulfates [CS; sulfated GalNAc(β1-4)GlcA/IdoA(β1-3)] are produced on a common GAG core: GlcA(β1-3)Gal(β1-3)Gal(β1-4)Xylβ-O-Ser.
• This core is synthesized by XYLT1/2, B4GalT-7 ('Gal transferase-I'), B3GalT6 ('Gal transferase-II') and B3GAT3 ('GlcA transferase-I').
• Thus, XYLT1/2 initiate the formation of heparan sulfates, chondroitin sulfates and dermatan sulfates.
• XYLTs are typical Type II enzymes with catalytic activity in the Golgi lumen. It is mostly expressed in Cis-Golgi but some activity may be present in late ER.
• Consensus sequence for XYLT1/2 include Serine with include Ser-Gly and a cluster of nearby acidic residues (e.g. Q-E-E-E-G-S-G-G-G-Q-K).
• XYLT2 is ubiquitously expressed. XYLT1 is rarely expressed alone with the possible exception of cartilage derived cells. Many tissue like kidney, brain, spleen, skeletal muscle etc. express both enzymes.
• XylT2 mice are viable, but develop biliary cysts and renal tubule dilation with accompanied liver and renal fibrosis at 4-5 months.